The last three probably aren’t interesting. However, if you are
interested in the GC (or SRE) implementation, then you should look
under Modules as
gcmodule.c and _sre.c are there. So are a bunch of
others.

Include isn’t particularly interesting.
Objects isn’t too
interesting either from the standpoint of learning about the
interpreter. Although the object implementations may be interesting
in their own right. Each object is in an unsurprising file named
something like: listobject.c or intobject.c.